Exhaust sensors are conventionally used in vehicles to sense the level of oxygen in the exhaust gases. These sensors detect changes in the exhaust gas content, i.e., when the content changes from rich to lean or lean to rich in relation to the air/fuel ratio. One known type of oxygen sensor is a flat plate oxygen sensor formed of various layers of ceramic and electrolyte materials laminated and sintered together with electrical circuit and sensor traces placed between the layers in a conventional manner. A typical co-sintered flat plate sensor element is disclosed in U.S. Pat. No. 5,433,830 to Kawai et al; and commonly assigned U.S. Pat. No. 5,395,506 to Duce et al.
Numerous attempts have been made to produce improved exhaust sensors. One such sensor is disclosed in commonly assigned U.S. Pat. No. 5,384,030 to Duce et al. This patent discloses an exhaust sensor having a substrate with a dielectric material, an electrolyte material, and a transition zone disposed therebetween. Another improved sensor is disclosed in U.S. Pat. No. 5,733,504 to Paulus et al. This patent addresses lean switch point by teaching the use of a pre-equilibration zone on an exhaust gas sensor to provide a catalytic site to catalyze less reactive components of the exhaust gas prior to the gas sample reaching the sensor's exhaust side electrode.
What is needed in the art is an improved exhaust sensor having improved performance, reduced sensitivity to processing, reproducibility and potentially higher manufacturing tolerances.